According to BussinessWire 2011 Wedding Statistics, the average number of wedding guests is 141. The average Jewish wedding is more than double that. The caveat is that the frum family is about 3 1/2 times the the non-jewish family. This means that the Family/Aquantence ratio is considerably smaller among Non-Jews.
If this convinces you to invite them, it shouldn’t.
Phobia aside, your husband is right.
Tell your business aquantinces fleetingly that it is a religious ceremony, and make no fuss about it.
Bring cakes to your office afterwards from the wedding.
Instead of spending $20 dollars on dining them, buy a 20 cake for each one. This should impress them enough to make up for there non-invite.
If you think this isn’t good enough, and that it can jeapordize your work atmosphere and parnassa, consult with a Rav, and refer back to you husband.